A floating type brake disc is structured by connecting a disc-like aluminum hub, and an annular stainless steel rotor coaxially arranged in an outer side of the hub by an elastic member.
A conventional floating type brake disc is provided with a hub “a” having semicircular recess portions “a1” in an outer peripheral edge portion leaving a space in a circumferential direction, and a rotor “b” having semicircular recess portions “b1” in an inner peripheral edge portion leaving a space in a circumferential direction, as shown in FIG. 21, and is prevented from coming off by butting the recess portion “a1” of the hub “a” to the recess portion “b1” of the rotor “b”, inserting a common pin “c” having a flange “c1a” in one end to a circular hole formed by the recess portions “a1” and “b1” via a washer as required, fitting and inserting a disc spring “c2” and a washer “c3” to another end “c1b” of the pin “c”, and thereafter expanding another end “c1b” of the pin “c” to an outer side so as to caulk in a disc shape. Thus, the floating type brake disc is structured by floatably connecting the hub “a” and the rotor “b” in a thrust direction. The disc spring “c2” is in contact with the hub “a” and the rotor “b” (refer, for example, to FIG. 2 in Japanese Unexamined Utility Model Publication No. 60-3333).
In order to avoid an interference between a wheel and the brake disc, an outer peripheral edge portion of the hub “a” is generally offset to an outer side in an axial direction (a thrust direction) via an intermediate portion “a2” which is linearly inclined along a radial direction with respect to an inner peripheral mounting portion to a side wheel.
In this conventional brake disc, a floating portion (a connection portion) is prevented from being rattle in the thrust direction by pressing and fixing the rotor to the flange portion of the pin from the thrust direction (a side surface of the rotor) by the disc spring or the like, and is prevented from being rattle in the radial direction by an assistance of the disc spring. A heat generated in the rotor gets away from the connection portion to the aluminum hub.
In the conventional brake disc, since the connection portion between the hub and the rotor by the pin is arranged at seven to ten positions, there is a problem that a number of the parts is much. For example, a seven-axis specification (seven-position connection specification) requires thirty parts (including (pin+disc spring+washer×2)×7+rotor+hub), and a ten-axis specification (ten-position connection specification) requires forty two parts (including (pin+disc spring+washer×2)×10+rotor+hub). Accordingly, an assembling man-hour thereof is increased, and a cost is increased.
In recent years, in connection with a cost reduction, a weight saving and the like, the number of the pins tends to be reduced. In the case that the number of the pins is reduced, there are generated a portion in which the heat of the rotor tends to be discharged, and a portion in which the heat tends to be kept. Accordingly, a thermal stress near a pierce hole formed on a sliding surface of the rotor becomes high, whereby a crack tends to be generated.
Further, in the conventional brake disc, a floating performance and an increase of spring setting load tend to be opposite to each other. Accordingly, the higher a set load (a fixing load) by the spring from the thrust direction is, the more advantageous the rattle prevention in the radial direction is, however, the floating performance in the thrust direction is deteriorated. Further, the disc spring is in contact with the hub and the rotor, however, since the thickness of the hub and the rotor have a dispersion within a tolerance, a deflection of the disc spring has a dispersion within the disc spring.
Further, since a constraint force from the thrust direction is strong, the brake disc is hard to adapt itself to brake pads at a time of being pinched by the brake pads so as to generate a thermal strain. Further, since the rotor is brought into contact with the flange side of the pin on the basis of the constrain from the thrust direction, it is necessary to improve an initial deflection accuracy. If the initial deflection accuracy is low, a part (having a large deflection) of the rotor is in contact with the pad during running (during rotation of the rotor), and a biased abrasion is generated. As a result, when applying the brake, a judder (an abnormal vibration) is caused by the biased abrasion.
In this case, since the brake disc tends to adapt itself to the pads by making the constraint force from the thrust direction weak, the floating performance is improved (the floating performance is improved so as to tend to adapt itself to the pads), however, the rattle in the radial direction tends to be generated. Accordingly, the rotor gives a shock to the pin/hub during running on a punishing road so as to cause a breakage of the hub.
Further, since the load of the brake disc corresponds to a non-suspended load (an unspring weight) applying a great influence to a steering stability of the vehicle, there is a tendency that a weight saving of the brake disc is intended, and a weight saving hole provided in the hub “a” and the rotor “b” is enlarged. However, since it is necessary to secure a certain degree of calorific capacity in the rotor portion, there is a limit to enlarge the weight saving hole. Accordingly, there is a great demand to enlarge the weight saving hole in the hub “a”, however, in the case that an area of the rib “a3” between the weight saving holes is reduced by enlarging the weight saving hole in the intermediate portion “a2”, a strength in a lateral direction (the thrust direction) of the hub “a” becomes weak, and a strength in a torsional direction becomes weak.
An object of the present invention is to provide a floating type brake disc which can improve a heat lowering performance and can widely reduce a number of parts, taking the conventional problems mentioned above into consideration.
Another object of the present invention is to provide a floating type brake disc which can absorb a shock applied to the hub from the rotor at a time of running on the punishing road, in addition to the advantage mentioned above.
The other object of the present invention is to provide a floating type brake disc which can improve a strength in a thrust direction and a torsional direction of the hub even in the case that the weight saving hole of the hub is enlarged, in addition to the advantages mentioned above.